Hmm, now I am thoroughly confused. You don't seem to have any values specified for WidthPx and HeigthPx in your example. Also you are pointing to another web page inside the application. My links were pointing to external url's maybe that makes the difference.

In fact when I change only the link in your example to Common\ExternalURL and set the URL value to "http://code.msdn.microsoft.com/FinancialFunctions" I get a really small preview window. Adding a fixed value to the two parameters above results in again a larger popup but as before, only a small portion at the top actually has the preview in it. I have attached your example with my changes.

Note, give that I am behind a fairly restrictive firewall which might be interfering with this component but if that were the cause I would expect to see nothing at all instead of this.

There is a small difference between those two usages...but makes all the difference.

Your usage: Popup_InfoBalloon pointing to a ExternalSite with external URL
Hugo's usage: Popup_InfoBalloon pointing to a internal page with the "magic" difference: The destination page have a table with two special css styles: DocumentPopup (table level), BodyPopup (cell level).
I dont know why but those 2 styles are both important for correctly "on the fly" size adusjtment.

The major problem is the use of external url because I remove the styles and the infoballon resizes good.

Maybe is not good to use external sites on info ballons because needs to load all the CSS from the site, cant understand why the infoballon dont resize maybe the styles from the site or the iframe used from the infoballon.